docker: Add installation instructions.

README.md

@@ -1,12 +1,12 @@
 # Eris Codebase Monitor
 
-### Summary
+## Summary
 
 Eris maintains an up-to-date set of reports for every file in a codebase.
 
-### Installation
+## Installation
 
-(Tested in Ubuntu 19.10)
+### Ubuntu (19.10)
 
     # git clone https://github.com/ahamilton/eris
     # cd eris
@@ -21,7 +21,15 @@ then to run:
 
     # eris <directory_path>
 
-### Tools
+### Docker
+
+    # git clone https://github.com/ahamilton/eris
+    # cd eris
+    # sudo docker build -t eris .
+    # mv eris-docker ~/bin
+    # eris-docker -h
+
+## Tools
 
 Extensions(98) | Tools(60)
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